Fructose metabolism in humans -- what isotopic tracer studies tell us

Objective: A review of fructose disposal and metabolism in humans based on isotope tracer studies.

Design: Narrative review (semi-systematic).

Setting: Various

Participants: Studies undertaken in adult humans at rest and during exercise. Studies included males and females, with some studies including obese subjects or subjects with Type 2 DM. The studies provided fructose in isolation, or bound (i.e. sucrose), or with other sugars (e.g. glucose, sucrose etc.)

Results: Studies on subjects at rest, suggested that between 30 and 59% of ingested fructose was oxidised within 3-6 hr. This would include not only direct oxidation of fructose, but also indirect oxidation via glucose, glycogen and lactate. Results of studies at rest suggest that between 29 and 54% of fructose is converted to glucose. No studies provide data for conversion of fructose to lactate at rest, although a study during exercise reported 28% of ingested fructose was converted to lactate. The extent to which fructose is converted to glycogen has not been studied using isotope tracer studies. Studies examining fructose conversion to lipid are fraught with problems eg. Inability to quantify DNL in adipose or muscle, however, conversion is suggested to be small.

Conclusions: This review provides a basic outline of how fructose is utilized after consumption by humans